1. Field of the Invention
This invention relates to transistor oscillators and, more particularly, to a high frequency, stable oscillator utilizing a transistor having an input reflection coefficient which is inductive at high frequencies and having a gain at high frequencies which is sufficient for oscillation.
2. Description of the Prior Art
Stable oscillators are frequently employed in equipment which must be insensitive to vibration. Such oscillators are used in microwave landing systems (MLS) for the guidance of aircraft. MLS receivers installed in aircraft assist in guiding the aircraft during landing by interpreting MLS signals provided by an MLS ground station located at the airport. The MLS receiver must generate an accurate oscillation frequency to insure reception of the MLS signals of the MLS ground station.
In the prior art, two forms of oscillators have been employed, one utilizing a resistive-capacitive feedback circuit, and the other utilizing a resonant tank circuit comprising a capacitor and an inductor. At high frequencies i.e. (400 MHz) the resistive-capacitive circuit is disadvantageous in that the loop gain may be too low to sustain oscillation, and in that if oscillation is obtained, the circuit Q is too low to hold the frequency with the desired accuracy. On the other hand, a tank circuit may not be utilized because it is vibration sensitive. Small dimensional changes appear in the inductor at the vibration frequencies with a consequential modulation of the oscillation frequency. The magnitude of the frequency dispersion due to such vibration degrades the performance of the oscillator and, consequently, the landing system.
Thus, a problem exists in that while the inductor is most useful in a high-Q tank circuit for accurately tuning the oscillator, the susceptibility to vibration results in an undesirable frequency modulation with a consequential degradation in the operation of the microwave landing system.